During operation, the cylinders of large internal combustion engines often create a heat gradient from the relatively cool intake side of the cylinder and the relatively hot exhaust side of the cylinder. This heat gradient may cause warping of the intake and exhaust valves if the gradient becomes too intense, thereby accelerating wear and potentially damaging the valves and valve seats. To combat these effects, valve rotators are commonly installed to rotate the valves during engine operation, which results in the valves being subjected to a more even distribution of heat. Rotation of the valve also provides a more even wear pattern for the valve and valve seat.
Valve rotators are frequently constructed in two parts, a housing that engages and is fixed relative to an end of the valve spring(s), and a body coupled to the valve stem. For every reciprocating movement of the valve, the body and the valve together rotate a small amount relative to the housing.
For higher performance and enhanced durability, valve springs are becoming increasingly hard and stiff. In response, the housing of the valve rotator assembly must also be hardened to resist premature wear on the surfaces of the housing that contact the spring. As a result of this hardening, the housing also becomes increasingly brittle and prone to cracking when worked. This issue is particularly troublesome in valve rotator assemblies in which an edge surface of the housing is cold rolled over a portion of the rotator body to form a locking bead that secures the two components together. Many times, the addition of the locking bead to a hardened housing by cold forming results in the part being cracked and/or rendered unusable.